U.S. patent application number 10/886008 was filed with the patent office on 2005-06-23 for process control scheme for cooling and heating compressible compounds.
This patent application is currently assigned to Dreyer's Grand Ice Cream, Inc.. Invention is credited to D'Arcangelis, Larry, Tapfer, Uwe.
Application Number | 20050132902 10/886008 |
Document ID | / |
Family ID | 34068220 |
Filed Date | 2005-06-23 |
United States Patent
Application |
20050132902 |
Kind Code |
A1 |
D'Arcangelis, Larry ; et
al. |
June 23, 2005 |
Process control scheme for cooling and heating compressible
compounds
Abstract
A process control scheme for use with an extruding apparatus for
cooling and heating aerated or compressible compounds that are
edible. Broadly, the process includes providing a mixture to an
inlet of the extruding apparatus, monitoring the pressure profile
across the extruding apparatus, moving the mixture through the
extruding apparatus with at least one auger while subjecting the
mixture to a thermo-dynamic process, automatically altering speed
of the at least one auger if the pressure profile across the
extruding apparatus is outside a predetermined range, and moving
the mixture through an outlet of the extruding apparatus. The
process may also include monitoring temperature of a thermodynamic
liquid, monitoring the load of an auger motor, and automatically
altering the temperature of the thermodynamic liquid and the load
of the auger motor if one of either the temperature of the
thermodynamic liquid and the load of the auger motor is outside a
predetermined range.
Inventors: |
D'Arcangelis, Larry; (South
San Francisco, CA) ; Tapfer, Uwe; (Oakland,
CA) |
Correspondence
Address: |
TOWNSEND AND TOWNSEND AND CREW, LLP
TWO EMBARCADERO CENTER
EIGHTH FLOOR
SAN FRANCISCO
CA
94111-3834
US
|
Assignee: |
Dreyer's Grand Ice Cream,
Inc.
Oakland
CA
|
Family ID: |
34068220 |
Appl. No.: |
10/886008 |
Filed: |
July 6, 2004 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
60485574 |
Jul 7, 2003 |
|
|
|
Current U.S.
Class: |
99/455 |
Current CPC
Class: |
B29C 48/83 20190201;
B29C 2948/92828 20190201; B29C 48/834 20190201; A23C 2260/152
20130101; A23G 9/20 20130101; B29C 2948/92895 20190201; A23G 9/285
20130101; B29C 48/03 20190201; B29C 2948/92704 20190201; B29C
2948/92952 20190201; B29C 2948/92514 20190201; B29C 48/92 20190201;
B29C 48/797 20190201; B29C 2948/9258 20190201; A23G 9/22
20130101 |
Class at
Publication: |
099/455 |
International
Class: |
A23C 003/04 |
Claims
What is claimed is:
1. A process for making a frozen novelty with an extruding
apparatus including at least one auger, the process comprising:
providing a compressible compound to an inlet of the extruding
apparatus; monitoring a pressure profile across the extruding
apparatus; moving the compressible compound through the extruding
apparatus with the at least one auger while subjecting the
compressible compound to a cooling process; automatically altering
speed of the at least one auger if the pressure profile across the
extruder apparatus is outside a predetermined range; and moving the
compressible compound through an outlet of the extruding
apparatus.
2. A process in accordance with claim 1 wherein the pressure
profile is monitored by one of measuring pressure at the inlet,
measuring pressure at the outlet, measuring pressure at at least
one point in between the inlet and the outlet, and using a function
of multiple pressure measurements.
3. A process in accordance with claim 1 further comprising
monitoring temperature of a heat transfer medium, monitoring load
of an auger motor, and automatically altering the temperature of
the heat transfer medium and the load of the auger motor if at
least one of either the temperature of the heat transfer medium or
the load of the auger motor is outside a predetermined range.
4. A process in accordance with claim 3 further comprising
monitoring pressure at the outlet and if the outlet pressure
exceeds a predetermined amount, then the predetermined range for
the heat transfer medium temperature is increased by a
predetermined level and the auger motor load is monitored and
controlled.
5. A process in accordance with claim 4 wherein the predetermined
level is 3 degrees F.
6. A process in accordance with claim 4 wherein the heat transfer
medium temperature is measured in predetermined time intervals and
the predetermined range for the heat transfer medium temperature is
increased in predetermined increments if the outlet pressure
continues to exceed the predetermined range.
7. A process in accordance with claim 6 wherein the heat transfer
medium temperature is measured every 30 seconds and the
predetermined range for the heat transfer medium temperature is
increased in 3 degrees F. increments if the outlet pressure
continues to exceed the predetermined range.
8. A process in accordance with claim 6 wherein once the outlet
pressure is back within the predetermined range for a predetermined
amount of time, the auger motor load is monitored and controlled
automatically.
9. A process in accordance with claim 3 wherein the heat transfer
medium is ammonia and the temperature monitored is an ammonia
evaporation temperature.
10. A process in accordance with claim 4 wherein the ammonia
evaporation temperature is measured as a function of ammonia
evaporation pressure.
11. A process in accordance with claim 1 wherein the frozen novelty
is ice cream.
12. A process in accordance with claim 1 wherein the frozen novelty
is frozen yogurt.
13. A process in accordance with claim 11 wherein the frozen
novelty is one of low fat ice cream having a fat content of 1%-8%,
non-fat ice cream, premium ice cream having a fat content in a
range of 9%-14%, or super premium ice cream having a fat content in
a range of 15%-20%.
14. A process in accordance with claim 1 wherein the frozen novelty
is one of sorbet, sherbet or melorene.
15. A process in accordance with claim 1 wherein the predetermined
range is dependent upon a flavor of the frozen novelty.
16. A process in accordance with claim 3 wherein the predetermined
ranges are dependent upon a flavor of the frozen novelty.
17. A process for making a frozen novelty with an extruding
apparatus having at least one auger, the process comprising:
providing a mixture to an inlet of the extruding apparatus;
monitoring a pressure profile across the extruding apparatus;
moving the mixture through the extruding apparatus with the at
least one auger while subjecting the mixture to a freezing process;
automatically altering speed of the at least one auger if the
pressure profile across the extruding apparatus is outside a
predetermined range; monitoring temperature of ammonia used as a
coolant by monitoring an ammonia evaporation temperature as a
function of ammonia evaporation; monitoring load of an auger motor;
automatically altering the temperature of the ammonia and the load
of the auger motor if at least one of either the temperature of the
ammonia and the load of the auger motor is outside a predetermined
range; and moving the mixture through an outlet of the extruding
apparatus.
18. A process in accordance with claim 17 wherein the pressure
profile is monitored by one of measuring pressure at the inlet,
measuring pressure at the outlet, measuring pressure at at least
one point in between the inlet and the outlet, and using a function
of multiple pressure measurements.
19. A process in accordance with claim 17 further comprising
monitoring pressure at the outlet and if the outlet pressure
exceeds a predetermined amount, then the predetermined range for
the coolant temperature is increased by a predetermined level and
the auger motor load is monitored and controlled.
20. A process in accordance with claim 19 wherein the predetermined
level is 3 degrees F.
21. A process in accordance with claim 19 wherein the coolant
temperature is measured in predetermined time intervals and the
predetermined range for the coolant temperature is increased in
predetermined increments if the outlet pressure continues to exceed
the predetermined range.
22. A process in accordance with claim 21 wherein the coolant
temperature is measured every 30 seconds and the predetermined
range for the coolant temperature is increased in 3 degrees F.
increments if the outlet pressure continues to exceed the
predetermined range.
23. A process in accordance with claim 22 wherein once the outlet
pressure is back within the predetermined range for a predetermined
amount of time, the auger motor load is monitored and controlled
automatically.
24. A process in accordance with claim 17 wherein the frozen
novelty is ice cream.
25. A process in accordance with claim 17 wherein the frozen
novelty is yogurt.
26. A process in accordance with claim 17 wherein the frozen
novelty is low fat ice cream.
27. A process in accordance with claim 17 wherein the predetermined
ranges are dependent upon a recipe of the frozen novelty.
28. A process in accordance with claim 19 wherein the predetermined
range is dependent upon a recipe of the frozen novelty.
29. A process in accordance with claim 28 wherein the predetermined
outlet pressure amount is dependent upon a recipe of the frozen
novelty.
30. A system for making a frozen novelty, the system comprising: an
extruding apparatus comprising at least one auger, at least one
auger motor, an inlet and an outlet; a central controller in
communication with the extruding apparatus; a graphical user
interface in communication with the central controller; a pressure
profile monitor in communication with the central controller; a
coolant temperature monitor in communication with the central
controller; and an auger motor load monitor in communication with
the central controller; wherein a user uses the graphical user
interface to select target points or target ranges for a pressure
profile, auger motor load and coolant evaporation temperature; and
wherein the central controller automatically adjusts appropriate
components if a target point or range is not met by a predetermined
amount.
31. A system in accordance with claim 30 wherein the coolant is
ammonia and the temperature monitor comprises an ammonia
evaporation pressure monitor.
32. A system in accordance with claim 30 wherein the pressure
profile monitor comprises at least one of an inlet pressure
monitor, an outlet pressure monitor, and a pressure monitor between
the inlet and the outlet, wherein the user selects a target
pressure or pressure range and the central controller automatically
adjusts operating parameters if the target point or range is not
met by a predetermined amount.
33. A process for altering temperature of a compressible or aerated
mixture with an extruding apparatus including at least one auger,
the process comprising: providing the mixture to an inlet of the
extruding apparatus; monitoring a pressure profile of the extruding
apparatus; moving the mixture through the extruding apparatus with
the at least one auger while subjecting the mixture to a
thermodynamic process; automatically altering speed of the at least
one auger if the pressure profile across the extruding apparatus is
outside a predetermined range; and moving the mixture through an
outlet of the extruding apparatus.
34. A process in accordance with claim 33 wherein the pressure
profile is monitored by one of measuring pressure at the inlet,
measuring pressure at the outlet, measuring pressure at at least
one point in between the inlet and the outlet, and using a function
of multiple pressure measurements.
35. A process in accordance with claim 33 further comprising
monitoring temperature of a heat transfer liquid, monitoring load
of an auger motor, and automatically altering the temperature of
the heat transfer liquid and the load of the auger motor if at
least one of either the temperature of the heat transfer liquid or
the load of the auger motor is outside a predetermined range.
36. A process in accordance with claim 35 further comprising
monitoring pressure at the outlet and if the outlet pressure
exceeds a predetermined amount, then the predetermined range for
the heat transfer liquid temperature is increased by a
predetermined level and the auger motor load is monitored and
controlled manually.
37. A process in accordance with claim 36 wherein the predetermined
level is 3 degrees F.
38. A process in accordance with claim 36 wherein the heat transfer
liquid temperature is measured in predetermined time intervals and
the predetermined range for the heat transfer liquid temperature is
increased in predetermined increments if the outlet pressure
continues to exceed the predetermined range.
39. A process in accordance with claim 38 wherein the heat transfer
liquid temperature is measured every 30 seconds and the
predetermined range for the heat transfer liquid temperature is
increased in 3 degrees F. increments if the outlet pressure
continues to exceed the predetermined range.
40. A process in accordance with claim 38 wherein once the outlet
pressure is back within the predetermined range for a predetermined
amount of time, the auger motor load is monitored and controlled
automatically.
Description
CROSS-REFERENCES TO RELATED APPLICATIONS
[0001] This application is a non-provisional application and claims
the benefit of Application No. 60/485,574, filed Jul. 7, 2003,
entitled "Process Control Scheme for Cooling and Heating
Compressible Compounds," (Attorney Docket No. 020903-020300U.S.),
the disclosure of which is incorporated herein by reference for all
purposes.
STATEMENT AS TO RIGHTS TO INVENTIONS MADE UNDER FEDERALLY SPONSORED
RESEARCH OR DEVELOPMENT
[0002] NOT APPLICABLE
REFERENCE TO A "SEQUENCE LISTING," A TABLE, OR A COMPUTER PROGRAM
LISTING APPENDIX SUBMITTED ON A COMPACT DISK
[0003] NOT APPLICABLE
BACKGROUND OF THE INVENTION
[0004] 1. Field of the Invention
[0005] The present invention relates to a process control scheme
for cooling and heating compressible compounds, and more
particularly, to a process control scheme for making a frozen
novelty such as ice cream, frozen yogurt, etc. with an extruding
apparatus.
[0006] 2. Description of the Prior Art
[0007] It is known to aerate a mix for the preparation of an ice
cream through the use of an aerating apparatus that generally
includes a rotating element that fits into the barrel of a
continuous ice cream freezer. This aerating apparatus is commonly
referred to as a dasher. Rotation of the dasher imparts a
mechanical energy into the mix in order to achieve aeration and
generate a fat network by aggregating some of the fat droplets.
This aggregation is necessary for product stability.
[0008] For many continuous industrial freezers, there are a variety
of dasher types available. These may be differentiated from each
other by the volume displaced within the freezer barrel that may be
assessed by simply filling the freezer barrel with a liquid, such
as water, and measuring defined by liquid displaced with the dasher
is fitted therein. A dasher described as a Series 80 indicates that
this rotating element occupies 80% of the available internal volume
of the freezer barrel so that only 20% of the space is available to
be occupied by the mix to be aerated. By contrast, a Series 15
dasher, also known in the art, demonstrates a displacement volume
of only 15% of the internal barrel volume, the remaining 85% being
available to be occupied by a mix to be aerated.
[0009] In conventional ice cream processing it is generally
accepted that higher displacement dashers such as the Series 80
give rise to high quality ice cream being highly churned (Ice Cream
5.sup.th Edition, W. S. Arbuckle et al., page 183) thus showing
optimal levels of fat de-stabilization, while at the same time
having product dryness, good meltdown resistance and product
hardness. These displacement dashers are therefore the standard
form of aerating means used in ice cream manufacture.
[0010] Traditional frozen aerated products such as ice cream
products contain approximately 8 to 12% fat in addition to
stabilizers and emulsifiers in order to provide the desired quality
product. However, it is now preferable to provide such products
that are low fat and that do not include the additives. To date,
products provided that are low fat and without added stabilizers
and emulsifiers have been inferior in quality in that they are fast
melting, have a low percentage of destabilized fat, and are
unstable to heat shock, and hence, quickly become very icy.
Furthermore, such products have a reduced creaminess
perception.
[0011] Cold extrusion of aerated compositions is known in the art
through the extrusion of a pre-aerated foam through a freezing
device. Pre-aeration has conventionally been undertaken through the
use of an aerating means in the form of a high displacement dasher.
The foam once aerated is then transferred to cold extrusion
apparatus. The ice cream extrusion freezer processes ice cream
produced in a standard ice cream freezer. The extrusion freezer
applies work to the product via shear forces generated by the
augers moving the product through the extrusion freezer barrel at
very low speeds while removing heat from the product with ammonia
as a refrigerant.
[0012] The residence time of the ice cream in the extrusion freezer
barrel and hence the amount of heat removed from the ice cream may
be controlled by varying the speed of the augers. Due to the
compressible nature of ice cream, a slower auger speed results in a
longer product residence time in the extrusion freezer barrel and
therefore greater heat transfer. The rate of heat transfer also
depends on the temperature difference between the ice cream and the
extrusion freezer ice cream barrel wall. The temperature of the
extrusion freezer ice cream barrel wall may be controlled by
regulating the temperature of the ammonia refrigerant in the
concentric ammonia barrel surrounding the inner extrusion ice cream
barrel. A colder ammonia temperature results in more heat being
removed from the ice cream moving through the barrel.
[0013] Until the present invention, it has not been possible to
make frozen novelties such as ice cream of adequate quality with an
extruder due to the thickening (or lack thereof) of the ice cream
while in the extrusion freezer and the varying pressures that
result by altering the temperature. Additionally, the recipe for
the frozen novelty affects operation, and ultimately quality of the
frozen novelty, of the extrusion freezer.
[0014] Several factors are considered in the design of an effective
automatic control system for the extrusion freezer including
optimizing the work/energy applied to the product, maximizing the
heat removed from the product, and leaving the product overrun
(volume ratio of mix and air in the ice cream) generated by the
standard ice cream freezer unaltered without exceeding system
pressures due to excessive ice cream viscosities.
SUMMARY OF THE INVENTION
[0015] The present invention provides a process control scheme for
use with an extruding apparatus for cooling and heating aerated or
compressible compounds that are edible. Broadly, the process
includes providing a mixture to an inlet of the extruding
apparatus, monitoring pressure at the input of the extruding
apparatus, moving the mixture through the extruding apparatus with
at least one auger while subjecting the mixture to a thermodynamic
process, automatically altering speed of the at least one auger if
the pressure profile across the extruder is outside a predetermined
range, and moving the mixture through an outlet of the extruding
apparatus. Preferably, the process also includes monitoring
temperature of a heat transfer medium, monitoring the load of an
auger motor, and automatically altering the temperature of the heat
transfer medium and the load of the auger motor if one of either
the temperature of the heat transfer medium and the load of the
auger motor is outside a predetermined range.
[0016] The present invention is especially suitable for making a
frozen novelty such as ice cream, frozen yogurt, etc. and thus, the
process preferably involves subjecting the mixture to a freezing
process as it moves through the extruding apparatus. Preferably,
the temperature of a coolant is monitored and the load of the auger
motor is also monitored. The temperature of the coolant and the
load of the auger motor are automatically altered if one of either
the temperature of the coolant and the load of the auger motor is
outside a predetermined range.
[0017] The present invention also provides a system for cooling and
heating aerated or compressible compounds that are edible. The
system includes an extruding apparatus comprising at least one
auger, at least one auger motor, and an outlet. A central
controller in communication with the extruding apparatus is
provided and a graphical user interface that is in communication
with the central controller is also provided. An inlet and outlet
pressure monitor may be provided that are in communication with the
central controller and a coolant temperature monitor is provided
that is in communication with a central controller. An auger motor
load monitor is provided that is in communication with the central
controller. In use, a user uses the graphical user input to select
target points or target ranges for the inlet pressure, auger motor
load and coolant evaporation temperature. The central controller
automatically adjusts appropriate components if a target point or
range is not met by a predetermined amount.
[0018] Other features and advantages of the present invention will
be apparent in view of the following detailed description of
preferred exemplary embodiments.
BRIEF DESCRIPTION OF THE DRAWINGS
[0019] FIG. 1 is a schematic illustration of a refrigeration system
using a process control scheme in accordance with the present
invention in a production cooling mode;
[0020] FIG. 2 is a schematic illustration of a refrigeration system
using a process control scheme in accordance with the present
invention in a shutdown mode;
[0021] FIG. 3 is a schematic illustration of a refrigeration system
using a process control scheme in accordance with the present
invention in a production pre-cool mode;
[0022] FIG. 4 is a schematic illustration of a refrigeration system
using a process control scheme in accordance with the present
invention in a production cooling mode; and,
[0023] FIG. 5 is an illustration of a graphics user interface (GUI)
Production Screen for a process control scheme in accordance with
the present invention.
DETAILED DESCRIPTION OF THE INVENTION
[0024] The present invention is directed to a process control
scheme for processing compressible and/or aerated compounds with an
extruder apparatus while subjecting the compound to a thermodynamic
process using a heat transfer medium. In a preferred embodiment,
the compound is a mixture that becomes a frozen novelty such as ice
cream, frozen yogurt, etc. Thus, for simplicity and clarity, the
present invention will be described with reference to making a
frozen novelty with an extruder apparatus, but those skilled in the
art will understand that there are many other uses for the present
invention and that it shouldn't be limited to the embodiments
described herein. For example, the present invention may be used
for extruding chocolate, or liquid aerated plastics or films.
[0025] FIG. 1 illustrates an extruder freezer system 100 that
includes an extruder freezer 101 that includes at least one auger
102. Preferably, there are two augers 102a, 102b that are side by
side. Extruder 107 includes a chamber 103 for cooling liquid such
as ammonia that substantially surrounds the barrel that includes
the augers. A liquid/gas separator 104 is provided that is in
communication with chamber 103. Extruder 107 receives a mixture
from ice cream freezer 105 at inlet 106. The finished product is
provided to an ingredient feeder 107 through outlet 108 for adding
ingredients such as, for example, chocolate, fruit, etc. A central
controller (not shown) is provided that controls operation of
extruder freezer system 100 via a graphical user interface (GUI).
System 100 includes a coolant suction valve 109. Valves 110-113 are
used for adding and removing coolant. Valves 125 and 126 are
preferably spring loaded safety relief valves.
[0026] Generally, the texture of ice cream is improved by applying
work/energy to the product while removing heat from the product.
The residence time of the product in the extrusion freezer barrel
and hence the amount of heat removed from the product may be
controlled by varying the speed of the augers. A slower auger speed
results in a longer product residence time in the extrusion freezer
barrel and therefore greater heat transfer. The rate of heat
transfer also depends upon the temperature difference between the
product and the extrusion freezer barrel wall. The temperature of
the extrusion freezer barrel wall can be controlled by regulating
the temperature of the ammonia refrigerant in the concentric
ammonia barrel surrounding the inner extrusion barrel. A colder
ammonia temperature results in more heat being removed from the
product moving through the barrel.
[0027] Preferably, the operation of the extruder freezer is
controlled by monitoring the inlet pressure with sensor 120 at
inlet 106 and the outlet pressure with sensor 124 at outlet 108 to
thereby monitor the pressure profile of the extruder freezer. The
pressure profile may be monitored by simply monitoring the pressure
at a single point, such as, for example, the inlet, the outlet, at
some point in between, or at multiple points. The pressure profile
may also be monitored as a function of multiple points, e.g., the
difference between the inlet pressure and the outlet pressure.
Additionally, preferably the operation of the extruder freezer is
further controlled by monitoring the load of auger motor 121 with
sensor 122. Finally, preferably the operation of the extruder
freezer is further controlled by monitoring the evaporation
temperature/pressure of the ammonia with sensor 123.
[0028] The inlet pressure is used in a
proportional-integral-derivative (PID) inlet pressure control loop.
The inlet pressure control loop compares the actual extruder
freezer inlet pressure with an inlet pressure set point entered at
the GUI screen illustrated in FIG. 5. The control loop
automatically varies the auger speed to maintain the inlet pressure
at the set point pressure. This loop is reverse acting, meaning
that the calculated error used by the control loop is:
[0029] Error=Process Variable-Set Point
[0030] where
[0031] Process Variable=Actual measured inlet pressure
[0032] Set Point=Inlet pressure set point entered from GUI
[0033] Because the PID control block increases its output signal,
in this case the auger speed, for an increase in error, the auger
speed increases for the case where the actual inlet pressure climbs
too high relative to the pressure set point and visa versa.
[0034] The present invention found that without the input pressure
control loop, the inlet pressure fluctuated substantially due to
events downstream in the process including ingredient feeder
settings and product flow path changes. Furthermore, because the
actual inlet pressures are typically high as a result of the
relatively slow auger speeds necessary to achieve a cold enough
product draw temperature given the available ammonia suction, these
fluctuations in inlet pressure would often result in very high
inlet pressures posing the threat of damage to the equipment.
[0035] The inlet pressure control loop enables the operator to
select a high enough inlet pressure set point to achieve the
desired product draw temperatures, given the available ammonia
suction, without the need of the operator to constantly monitor and
adjust for pressure fluctuations caused by downstream disturbances.
Furthermore an inlet pressure set point is selected that works for
different ice cream flow rates and for different ice cream
formulations since the extrusion freezer auger speed varies based
primarily on the inlet pressure independent of the product flow
rate and viscosity.
[0036] The auger motor load control preferably includes two cascade
PID control loops: an auger motor load PID control loop and an
ammonia evaporation temperature PID control loop.
[0037] The auger motor load control loop preferably compares the
actual motor load (preferably by measuring amps) with the load set
point entered from the GUI screen illustrated in FIG. 5. The output
of this control loop is tied to the set point of the ammonia
evaporation temperature control loop which automatically varies the
ammonia suction control valve to indirectly maintain the auger
motor load at the load set point. The auger motor load control loop
is forward acting, meaning that the calculated error used by the
control loop is:
[0038] Error=Set Point-Process Variable
[0039] where
[0040] Process Variable=Actual auger motor load
[0041] Set Point=Load set point entered from GUI
[0042] The control loop output, and hence the ammonia evaporation
temperature control loop set point, increases for the case where
the actual motor load is too low relative to the load set point and
visa versa. Note that the ammonia evaporation temperature set point
is preferably scaled such that an increase in set point translates
to a colder setting (scaled as +20.degree. F. To -43.degree. F.).
Therefore as the auger motor load control loop output increases as
the ammonia evaporation temperature set point gets colder.
[0043] The auger motor load control loop is preferably cascaded
with the ammonia evaporation temperature control loop so that the
evaporation temperature control loop can clamp the ammonia
evaporation temperatures to within ammonia vessel 103 temperature
rating. Although it may be much simpler to allow the auger motor
control loop output to directly modulate the ammonia suction
control valve, the resulting evaporation temperature would depend
on the available suction pressure at any given moment, which could
result in an evaporation temperature colder than the vessel
rating.
[0044] The ammonia evaporation temperature control loop compares
the actual evaporation temperature (calculated from the evaporation
pressure signal 123) with the evaporation temperature set point
generated from the cascaded auger motor load control loop. The
control loop automatically varies the ammonia suction control valve
position to maintain the evaporation temperature at the set point
temperature. This loop is also forward acting, meaning that the
calculated error used by the control loop is:
[0045] Error=Set Point-Process Variable
[0046] where
[0047] Process Variable=Actual ammonia evaporation temperature
[0048] Set Point=Evaporation temperature set point generated by
auger motor load loop
[0049] Therefore the suction control valve position increases in
the case where the actual evaporation temperature is too warm
relative to the temperature set point and visa versa. One would
initially think that this loop should be reverse acting however,
because the set point for this loop is scaled in decreasing order
(+20.degree. F. To -43.degree. F.) a forward acting loop is
used.
[0050] Because high extruder freezer outlet pressures may occur due
to high viscosity product as well as downstream process changes, a
high outlet pressure warning alarm is preferably interlocked with
the auger motor load control loops. If a high outlet pressure
warning alarm occurs, then the auger motor load control loop is
automatically switched to a manual control mode and the ammonia
evaporation temperature control loop set point is increased to a
warmer setting by preferably 3.degree. F. This temperature may be
higher or lower as desired. The evaporation temperature is
preferably monitored in 30 second intervals (once again this may be
higher or lower as desired) and the temperature set point increased
by 3.degree. F. increments (once again this may be higher or lower
as desired) if the high pressure condition still exists. If the
high outlet pressure condition is cleared for preferably 3 minutes
then the auger motor load control loop switches back to an
automatic control mode.
[0051] Preferably, there are three operating modes for the extruder
freezer: Shutdown Mode, Production Mode and CIP Mode.
[0052] An operator may switch to Shutdown Mode from the GUI.
Additionally, the system may automatically switch to Shutdown Mode
due to a system alarm. As may be seen in FIG. 2, during Shutdown
Mode, the liquid ammonia solenoid valves close (if open), the
ammonia suction control valve closes, and the ammonia drain valve
opens. Preferably, after a 5 second delay the ammonia hot gas valve
opens.
[0053] The operator ia able to switch to Production Mode from the
GUI. The extruder freezer preferably stays idle (augers off) until
ice cream is detected at the inlet of the extruder freezer. When
the low operating pressure set point is exceeded then the augers
run at a set speed based on the loaded recipe. If the inlet
pressure has remained above the low operating set point with the
auger running for 30 seconds then the system preferably
automatically initiates a refrigeration startup. Production Mode
has 3 control loops: Inlet Pressure Control, Auger Motor Load
Control, Ammonia Evaporation Temperature Control.
[0054] Preferably, Production Mode has 2 sub modes: Pre-Cool Mode
and Cooling Mode. Production Mode preferably always starts in
Pre-Cool sub mode.
[0055] In the Pre-cool mode, the auger motor control and
evaporation temperature control are preferably both in a manual
mode when the system enters Pre-cool mode. As may be seen in FIG.
3, the fast fill liquid ammonia valve 111, preferably using high
pressure warm liquid ammonia to avoid thermally shocking the empty
ammonia vessel, automatically opens filling the extruder freezer
ammonia vessel. When the level in the ammonia vessel reaches the
liquid ammonia control level switch, then the valve preferably
automatically closes. The ammonia suction control valve preferably
opens 20% while the vessel is filling with liquid ammonia. When the
level in the ammonia vessel reaches the liquid ammonia control
level switch, then the auger motor load control and ammonia
evaporation temperature control preferably switch to Automatic
Mode. In Automatic Mode the ammonia suction control valve position
preferably varies to regulate the ammonia evaporation suction
temperature to the set point generated by the auger motor load
control loop. The auger motor load control set point may be changed
from the GUI at this time if needed.
[0056] Preferably, once filled to the liquid ammonia control level
switch with warm liquid ammonia, the control fill liquid ammonia
valve 112, preferably using -40 degree pumped liquid ammonia, opens
when the liquid ammonia level in the vessel drops below the liquid
ammonia control level switch and closes when the level exceeds the
liquid ammonia control level switch. Debounce timers are preferably
used on the liquid ammonia control level switch to keep the control
fill liquid ammonia valve from chattering. If the auger motor load
control loop drives the ammonia evaporation temperature control
loop set point to a setting preferably warmer than 0 degrees
Fahrenheit, then preferably only warm liquid ammonia is used to
maintain the vessel liquid ammonia level.
[0057] Preferably, the inlet pressure control remains in Manual
Mode with the augers running at a constant speed set by the Auger
Speed Set Point. The auger speed set point may be changed at
anytime during Pre Cool Mode from the GUI. Once the vessel is
filled to the liquid ammonia control level switch, the inlet
pressure control may be switched between Manual and Automatic Modes
from the GUI.
[0058] In the cooling mode after the extruder freezer ammonia
vessel has been filled to the liquid ammonia control level switch
level at least once and the ammonia evaporation temperature in the
vessel is cold enough, preferably below 15 degrees Fahrenheit, then
the system preferably automatically switches to Cooling Mode, as
may be seen in FIG. 4. The auger motor load control set point
preferably may be changed at anytime during Cooling Mode from the
GUI. The load set point is preset based upon the loaded recipe. The
ammonia suction control valve continues to regulate the ammonia
evaporation temperature in the vessel to the evaporation
temperature set point generated by the auger motor load control
loop.
[0059] The control fill liquid ammonia valve, preferably using -40
degree pumped liquid ammonia, opens when the liquid ammonia level
in the vessel drops below the liquid ammonia control level switch
and closes when the level reaches the liquid ammonia control level
switch. If the auger motor load control loop drives the ammonia
evaporation temperature control loop set point to a setting
preferably warmer than 0 degrees Fahrenheit, then only warm liquid
ammonia is used to maintain the vessel liquid ammonia level.
[0060] The inlet pressure control switches to Automatic Mode when
the system switches to Production Cooling Mode. In automatic mode
the auger speed varies to regulate the extruder freezer inlet
pressure. The inlet pressure set point preferably may be changed at
anytime during Cooling Mode from the GUI. The inlet pressure set
point is preset based on the loaded recipe. The inlet pressure
control preferably may be switched between Manual and Automatic
Modes from the GUI at any time during Cooling Mode. Once in Manual
Mode the auger speed set point preferably may be manually
adjusted.
[0061] Preferably, if the extruder freezer outlet pressure is too
high (Outlet High Pressure Warning Set Point), then an alarm is
generated on the GUI, the auger motor load control switches to
Manual Mode, and the ammonia evaporation temperature set point
automatically increases by 3 degrees Fahrenheit in an attempt to
reduce the outlet pressure to an acceptable level. The outlet
pressure is reevaluated preferably 30 seconds after each
evaporation temperature set point change and adjusted again if
necessary. These values may be changed if desired. Preferably, if
the extruder freezer outlet pressure high warning condition has
cleared for 3 minutes (or longer or shorter if desired), then the
auger load control loop switches back to Automatic Mode.
[0062] The parameters for operation and control of the system
generally depend upon the compound moving through the extruder
freezer. In the preferred embodiment, this is generally dependent
upon the recipe for the frozen novelty.
[0063] Recipe handling is an integral component of the control
system. The recipe system stores recipes that preferably include a
recipe name, recipe initial auger speed, recipe initial inlet
pressure set point, and auger motor load set point. The GUI recipe
menu preferably allows the operator to select an existing recipe,
edit an existing recipe, delete an existing recipe, add a new
recipe, and save the current extruder freezer settings to the
current selected recipe.
[0064] Other embodiments and features of a control system in
accordance with the present invention will be described in the
following paragraphs.
[0065] In one embodiment, the extrusion freezer control system
design allows the operator to set the auger speed and ammonia
evaporation temperature set points from a computer display located
on the freezer. The operator typically sets the auger speed set
point as slow as possible with the coldest possible ammonia
evaporation temperature to try and achieve the coldest possible ice
cream draw temperature and to maximize the auger motor power
demand. The minimum auger speed is usually limited by the high
pressures at the extrusion freezer inlet and outlet resulting from
the increased ice cream viscosity in the extrusion freezer.
[0066] The auger speed set point in revolutions per minute (RPM),
entered on the computer display by the operator, is converted to a
corresponding speed command signal to the variable frequency drive
that controls the auger motor. The variable frequency drive varies
the frequency and voltage to the motor based on the speed command
signal therefore varying the auger motor speed.
[0067] The auger speed control is preferably "open-loop" control;
that is there is no feedback signal from the motor to tell the
controller how fast the auger motor is actually running. Tests
performed with encoder feedback from the auger motor to the
controller indicate that the fluctuations in the auger motor speed
at set frequency command signals from the variable frequency drive
are negligible and therefore an open-loop design is implemented to
reduce the complexity of the auger speed control system.
[0068] The ammonia evaporation temperature controller automatically
regulates the evaporation temperature of the ammonia in the outer
ammonia barrel surrounding the extrusion freezer ice cream barrel.
The operator enters an evaporation temperature set point in degrees
Celsius (.degree. C.) from the computer display and the controller
automatically modulates a control valve in the ammonia suction line
to regulate the ammonia evaporation temperature in the extrusion
freezer ammonia barrel.
[0069] Unlike the auger speed control, the ammonia evaporation
temperature control is preferably a "closed-loop" controller; that
is, the actual ammonia evaporation temperature is fed back to the
controller. The feedback signal is actually a pressure signal from
a sensor located in the ammonia suction line between the extrusion
freezer ammonia barrel and the modulating control valve. The
controller utilizes internal ammonia look-up tables to convert the
evaporation pressure signal to a corresponding temperature.
[0070] A pressure sensor is preferably used instead of a
temperature sensor to remove the lag time inherent in temperature
measurement. A diagram of the ammonia evaporation temperature
control system is shown in the following diagram, where:
[0071] PV--Actual ammonia evaporation temperature (-57.degree. C.
to +27.degree. C.)
[0072] SP--Set point temperature entered by operator (-42.degree.
C. to -6.degree. C.)
[0073] CV--Ammonia suction control valve position (0 to 100%) 1
[0074] The evaporation temperature controller preferably utilizes a
proportional-integral (PI) control algorithm as shown in the
following diagram. The controller uses this algorithm to
continuously calculate the control variable (CV) based on the error
between the process variable (PV) and set point (SP). The ammonia
evaporation temperature controller action is reverse acting, which
means that the error calculated by the PI algorithm is equal to the
process variable minus the set point (PV-SP). Therefore, because a
larger error results in a greater CV output, as the actual ammonia
evaporation temperature gets warmer (PV increases) the control
valve opens more (CV increases) to reduce the evaporation
temperature.
[0075] This control system design provides a suitable method of
controlling the extrusion freezing process. The computer display
provides an efficient and easy-to-use interface for the operator to
the control the process. The operator typically sets the auger
speed set point as slow as possible with the coldest possible
ammonia evaporation temperature to try and achieve the coldest
possible ice cream draw temperature and to maximize the energy/work
input to the product.
[0076] In another embodiment, if an extrusion freezer high inlet or
outlet pressure warning alarms occurs, the controller automatically
increases the auger speed set point and notifies the operator that
an automatic auger speed set point adjustment has been made. The
high pressure alarms are preferably monitored on 30 second
intervals and the auger speed set point is preferably increased by
0.2 RPM increments if the high pressure condition still exists. By
increasing the auger speed the residence time of the product in the
extruder barrel decreases resulting in a lower extruded product
viscosity and therefore lower system pressures.
[0077] With this embodiment, interlocking the auger speed control
and the high pressure alarm at the outlet of the standard ice cream
freezer (inlet to the extrusion freezer) greatly reduces the number
of undesired system shutdowns. The high pressure interlock may not
circumvent shutdowns in all cases, particularly when the operator
reduces the auger speed rapidly while the extruded product has
already achieved a high viscosity.
[0078] Interlocking the auger speed control with the high pressure
alarm at the outlet of the extrusion freezer has shown success.
Although over time the extruded ice cream viscosity decreases due
to a shorter residence time in the extruder barrel, the immediate
result of increasing the auger speed is to increase the pumping
action of the augers and therefore increase the extrusion freezer
outlet pressure even more. Because the outlet pressure is already
close to the system shut down pressure this increased pumping
action often results in a system shutdown.
[0079] Analyzing empirical data during this phase of testing
reveals that measuring the motor torque required is more critical
to the process and equipment sizing than measuring the required
motor power. The correlation between motor power and auger speed
indicates that the motor power demand increases little with slower
auger speeds and also that less than fifty percent of the motor
power capacity is being utilized. This incorrect observation has
led to downsizing the auger motor and additionally downsizing the
motor gearbox. Unfortunately it was later discovered that the
torque demand on the augers exceeded the full load capacity of the
new downsized motor. Further analysis reveals that the torque
demand on the auger motor is typically near the full load capacity
of the motor and that although the motor power increases little due
to slower auger speeds, the motor torque demand (represented by
motor amp draw) increases to a greater degree as the augers run
slower and the extruded ice cream viscosity increases. This is due
to the fact that the motor torque is directly proportional to the
motor power and inversely proportional to the motor speed:
T.varies.P/w (1)
[0080] where,
[0081] T--Motor Torque
[0082] P--Motor Power
[0083] w--Motor Speed
[0084] Therefore, although the motor power remains relatively
constant, the motor torque rapidly increases as the speed
decreases.
[0085] In a further embodiment, the control system design is
interlocks the extrusion freezer outlet pressure high alarm with
the ammonia evaporation temperature control instead of the auger
speed control.
[0086] Additionally the auger speed control is integrated into a
new auger motor load control algorithm used to regulate the load
(amps) on the auger motor and hence the amount of energy/work put
into the product.
[0087] If an extrusion freezer high outlet pressure warning alarms
occurs, the controller automatically increases the ammonia
evaporation temperature set point (warmer setting) and notifies the
operator that an automatic temperature set point adjustment has
been made. The high pressure alarm is preferably monitored on 30
second intervals and the evaporation temperature set point is
increased by 3.degree. C. increments if the high pressure condition
still exists. By increasing the evaporation temperature the heat
transfer rate from the product to the surrounding ammonia is
decreased resulting in a lower product viscosity and therefore a
lower extrusion freezer outlet pressure.
[0088] The auger motor load controller preferably automatically
regulates the auger motor load by varying the speed of the augers.
The operator enters a load set point in percent from the computer
display, where 100% equals the full load amp capacity of the auger
motor, and the controller automatically varies the auger speed, and
hence the residence time of the ice cream in the extrusion freezer
barrel, to regulate the load on the auger motor.
[0089] Similar to the ammonia evaporation temperature control, the
auger motor load control is a "closed-loop" controller. That is,
the actual auger motor load (amps) is fed back to the controller.
The auger motor load controller utilizes a proportional-integral
(PI) control algorithm. 2
[0090] where,
[0091] PV--Actual auger motor load (0 to 100%)
[0092] SP--Set point auger motor load entered by operator (0 to
100%)
[0093] CV--Auger speed (25 to 100%)
[0094] The controller uses this algorithm to continuously calculate
the control variable (CV) based on the error between the process
variable (PV) and set point (SP). Like the ammonia evaporation
temperature controller, the auger motor load controller action is
also reverse acting, which means that the error calculated by the
PI algorithm is equal to the process variable minus the set point
(PV-SP). Therefore, because a larger error results in a greater CV
output, as the actual auger motor load increases (PV increases) the
auger speed increases (CV increases) to reduce the load. A higher
auger speed results in a shorter product residence time in the
extrusion freezer barrel resulting in a lower ice cream viscosity
and therefore a lower auger motor load.
[0095] An additional feature of the auger motor load controller is
the capability of switching the controller between manual and
automatic control modes from the computer display. In manual mode
the auger speed control behaves as an open-loop controller and the
operator may manually adjust the auger speed set point as described
previously.
[0096] Note that the interlock between the auger speed control and
the high pressure alarm at the outlet of the standard ice cream
freezer (inlet to the extrusion freezer) remains functional in this
embodiment. Should a high inlet pressure alarm occur, the auger
motor load controller automatically switches to manual mode and the
auger speed is automatically adjusted as described previously. Once
the high pressure alarm incident has cleared for preferably at
least 3 minutes, then the auger motor load controller automatically
switches back to automatic mode and resumes regulation of the auger
motor load by varying the auger speed. Moving the extrusion freezer
high outlet pressure alarm interlock from the auger speed control
to the ammonia evaporation temperature control helps to reduce the
number of undesired system shutdowns. This high pressure interlock
may not circumvent shutdowns in all cases, particularly when a
disturbance downstream of the extrusion freezer causes a rapid
increase in pressure.
[0097] The addition of an auger motor load controller allows the
system to automatically adjust the auger motor speed to achieve a
desired auger motor load and hence control the work/energy input to
the product. A motor load set point of 100% may be entered from the
computer display and the control system maximizes the work input to
the product without exceeding the load capacity of the auger
motor.
[0098] This control system design works well on a pilot scale when
the operators are in close proximity of the extrusion freezer and
also hand filling the ice cream cartons. It is observed on a
production scale that the operators are frequently walking long
distances to check the extrusion freezer and make adjustments to
ensure that an undesired shutdown does not occur due to high system
pressures. High downstream disturbances due to filling equipment
problems and long pipe runs to the liquefier often create these
high pressures scenarios. Selecting a load set point that generates
the same corresponding system pressure at different ice cream flow
rates and for different ice cream formulations is impossible and
therefore the operator has no method of selecting extrusion freezer
settings that are robust enough to respond to all system pressure
disturbances.
[0099] In another embodiment, the auger motor load controller is
decoupled from the speed control and integrated with the ammonia
evaporation temperature control. Additionally, a new inlet pressure
controller is added to regulate the extrusion freezer inlet
pressure by varying the auger speed.
[0100] Thus, the auger motor load controller cascades with the
ammonia evaporation temperature controller. This cascaded control
generates a master slave relationship in which the output of the
auger motor load controller is used to manipulate the set point of
the evaporation temperature controller. In this control scheme the
operator enters the auger motor load set point from the computer
display and the system regulates the motor load by varying the
ammonia evaporation temperature set point.
[0101] The cascaded controller is as follows: 3
[0102] where,
[0103] Auger Motor PI Control Block:
[0104] PV--Actual auger motor load (0 to 100%)
[0105] SP--Set point auger motor load entered by operator (0 to
100%)
[0106] CV--0 to 100% scaled (-6.degree. C. to -42.degree. C.)
[0107] Ammonia Evaporation Temperature PI Control Block:
[0108] PV--Actual ammonia evaporation temperature (-57.degree. C.
to +27.degree. C.)
[0109] SP--Set point temperature from auger motor load controller
(-6.degree. C. to -42.degree. C.)
[0110] CV--Ammonia suction control valve position (0 to 100%)
[0111] In this cascaded control scheme the auger motor load
controller action is forward acting, which means that the error
calculated by the PI algorithm is equal to the set point minus the
process variable (SP-PV). Therefore, because a larger error results
in a greater CV output, as the actual auger motor load increases
(PV increases) the control variable decreases, resulting in a
warmer temperature set point to the evaporation temperature
controller, to reduce the load.
[0112] Similarly the ammonia evaporation temperature controller
action is forward acting. Therefore as the actual ammonia
evaporation temperature gets warmer (PV increases) the control
valve opens more (CV increases) to reduce the evaporation
temperature. One would initially think that this loop should be
reverse acting however, because the set point for this loop is
scaled in decreasing order (-6.degree. C. to -42.degree. C.) a
forward acting loop is used.
[0113] The reason for cascading the controllers is to protect the
extrusion freezer ammonia barrel from reaching temperatures colder
than the temperature rating of the barrel. The evaporation
temperature controller clamps the ammonia evaporation temperature
to within the ammonia vessel temperature rating (e.g. -50.degree.
C.). Although it would be much simpler to allow the auger motor
controller to directly modulate the ammonia suction control valve,
the resulting evaporation temperature would then depend on the
available suction pressure at any given moment and could result in
an evaporation temperature colder than the vessel rating.
[0114] The extrusion freezer high output pressure alarm interlock
preferably remains in effect in this embodiment. Should a high
outlet pressure alarm occur, the auger motor load controller
automatically switches to a manual mode and the evaporation
temperature controller set point is automatically adjusted as
described previously. Once the high pressure alarm incident has
preferably cleared for at least 3 minutes then the auger motor load
controller automatically switches back to automatic mode and
resumes regulation of the auger motor load by varying the ammonia
evaporation temperature controller set point.
[0115] In another embodiment, an extrusion freezer inlet pressure
controller regulates the pressure at the inlet of the extrusion
freezer by varying the auger speed. The operator enters an inlet
pressure set point in Bars from the computer display and the
controller automatically varies the auger speed to regulate the
inlet pressure.
[0116] The inlet pressure control is a "closed-loop" controller.
That is, the actual extrusion freezer inlet pressure is fed back to
the controller. The inlet pressure controller utilizes a
proportional-integral (PI) control algorithm as shown: 4
[0117] where,
[0118] PV--Extrusion freezer inlet pressure (0 to 17 Bars)
[0119] SP--Set point inlet pressure entered by operator (0 to
17%)
[0120] CV--Auger speed (25 to 100%)
[0121] The extrusion freezer inlet pressure controller action is
reverse acting. Therefore, because a larger error results in a
greater CV output, as the actual inlet pressure increases (PV
increases) the auger speed increases (CV increases) to reduce the
pressure.
[0122] The inlet pressure controller has the capability of manually
switching the controller between manual and automatic control modes
from the computer display. In manual mode the auger speed control
behaves as an open-loop controller and the operator may manually
adjust the auger speed set point as described previously.
[0123] The addition of the extrusion freezer inlet pressure
controller dramatically increases the robustness of the of the
extrusion freezer control system, particularly in responding to
system pressure disturbances. This in turn results in less operator
interaction with the extrusion freezer and more time for the
operator to perform the tasks necessary in a full scale production
environment.
[0124] Furthermore an inlet pressure set point is selected that
works for different ice cream flow rates and for different ice
cream formulations since the extrusion freezer auger speed varies
as a function of the inlet pressure independent of the product flow
rate and viscosity. The inlet pressure controller also effectively
responds to pressure changes downstream of the extrusion freezer,
due to disturbances and increased product viscosity, since the
downstream pressure changes affect the extrusion freezer inlet
pressure as well.
[0125] The auger motor load/ammonia evaporation temperature
cascaded controller allows the system to automatically adjust the
ammonia evaporation temperature surrounding the extrusion freezer
ice cream barrel to achieve a desired auger motor load and hence
control the work/energy input to the product. The cascaded
controller is very effective in controlling the auger motor load
although using the evaporation temperature to control the auger
motor load results in a slower response time than the speed
controller due to the large thermal lag behavior of the large mass
of the steel extrusion system.
[0126] The control system of the present invention provides a
super-cooled product exiting the extrusion freezer system. This
super-cooled product does not need to spend time in a cooling
tunnel or hardening system prior to palleting and shipment as is
required of other frozen products produced in various ways.
[0127] As noted previously, the present invention may be used for
extruding chocolate, or liquid aerated plastics or films. Thus, for
chocolate extrusion, the chocolate may be heated to generally
around 110 degrees F. as it moves through an extruder or other
apparatus. For liquid aerated plastics or films, they are heated to
around 400 degrees F. In both instances they are then preferably
moved through a second extruder and cooled.
[0128] The foregoing descriptions of specific embodiments of the
present invention have been presented for purposes of illustration
and description. They are not intended to be exhaustive or to limit
the invention to the precise forms disclosed, and obviously many
modifications and variations are possible in light of the above
teaching. The embodiments were chosen and described in order to
best explain the principles of the invention and its practical
application, to thereby enable others skilled in the art to best
utilize the invention and various embodiments with various
modifications as are suited to the particular use contemplated. It
is intended that the scope of the invention be defined by the
claims appended hereto and their equivalents.
* * * * *